Discharge-based photo ionisation detector for use with a gas chromatography system

A discharge-based photo ionisation gas detector for analysing a gas sample, comprising:

• a discharge zone configured to receive a flow of a discharge gas therethrough and generate a plasma from said discharge gas, the discharge zone having an outlet allowing optical radiation out of the discharge zone;
• a plasma-localizing mechanism configured to apply a plasma-localizing field across the discharge zone and positioned such that the plasma-localizing field localizes the plasma within the discharge zone in alignment with said outlet;
• and
• an ionisation zone configured to receive a flow of the gas sample therethrough, the ionisation zone having an inlet allowing the optical radiation from the discharge zone into the ionisation zone to photo ionise the gas sample.

A method of analysing a gas sample from a chromatography column, comprising:

• a) providing a discharge-based photo ionisation gas detector having a discharge zone and an ionization zone;
• b) splitting the gas sample into a first sample stream and a second sample stream;
• c) circulating the first sample stream through the discharge zone and applying a plasma-generating field across the discharge zone to generate a plasma from said first sample stream, the plasma emitting optical radiation;
• d) circulating the second sample stream through the ionisation zone and exposing said second sample stream to the optical radiation from the discharge zone, thereby generating an ionisation current by photo ionisation of the second sample stream by said optical radiation;
• and
• e) measuring said ionisation current.

A method of analysing a sample gas stream, comprising:

• a) providing a discharge-based photo ionisation gas detector having a discharge zone and an ionization zone;
• b) circulating a discharge gas stream through the discharge zone, the discharge gas stream comprising a carrier gas and impurity peaks time-separated by a chromatography column;
• c) applying a plasma-generating field across the discharge zone during interstitial moments between said impurity peaks in the discharge gas stream circulating through the discharge zone, thereby generating a plasma from the carrier gas in said discharge gas stream, the plasma emitting optical radiation;
• d) circulating the sample gas stream through the ionisation zone in synchronicity with the generation of the plasma in the discharge zone and exposing said sample gas stream to the optical radiation from the discharge zone, thereby generating an ionisation current by photo ionisation of the sample gas stream by said optical radiation;
• and
• e) measuring said ionisation current.